Semi-Stupid Question about the Robe of Vecna

Ok, so I am, yet again, going to play this masterpiece of a game. But this time, instead of some type of fighter or Fighter/Mage, I going to be a Cleric/Mage. So I was wondering if the Robe of Vecna's -4 to spellcasting would include Clerical Spells in addition to the Mage Spells it obviously effects. Well, thanks for any answers, and bye for now!